The present invention relates in general to an oxygen sensor for measuring the oxygen concentration in a fluid, the sensor being of the type having a layer of an oxygen ion conductive solid electrolyte. More specifically, the present invention is concerned with a so-called flat thin film type oxygen sensor which is suitable for measuring the oxygen concentration in an engine exhaust gas.
It is known that the flat thin film type oxygen sensors using a flat thin film solid electrolyte show better performance in EMF (electromotive force) characteristic and responsiveness as compared with tubular type oxygen sensors which use a tubular solid electrolyte. Some of these sensors have however a poor durability. In fact, it often happens that mutually attached element layers which form the thin film oxygen sensor come off or peel off from one another during the practical usage thereof.